While hydraulic systems have found numerous applications and in accordance with those applications taken many forms and constructions, all include the basic components of a closed fluid system which is filled with a generally incompressible fluid and which is coupled to a positive discharge pump for imparting a pressure to and producing flow in the .confined hydraulic fluid within the system. The system further includes a valve arrangement which controls the flow of pressurized fluid to one or more hydraulic cylinders. The latter varies substantially in construction but generally comprises an inner chamber or cylinder which supports a movable piston coupled to a piston rod. Means are provided for applying the fluid under pressure via the valve system to move the piston in the desired direction and thereby move the piston rod and accomplish the mechanical work output of the system. Thus, in its basic use, the hydraulic system is operative using the pump to provide fluid under pressure within the system while an operator manipulates the valve arrangement to control the motions of the various hydraulic cylinders within the system.
Hydraulic systems have become capable of producing great mechanical power and manipulating very sizeable loads. In accomplishing this power handling capability, many hydraulic systems function with a large number of hydraulic cylinders and utilize pumps providing very substantial fluid pressures. Because of the use of a hydraulic fluid which is generally incompressible and because rapid volume changes are produced as the system functions in Its normal manner, the system is subject to abrupt pressure changes and flow surges which must be accommodated and controlled if the system is to function reliably.
This problem of compensating for and controlling sudden pressure changes and flow surges within fluid systems is not unique to hydraulic power systems. Such problems also arise in pipeline distribution operations in which a generally incompressible fluid is being pumped under pressure through a network of pipelines to various destinations.
To meet the problem of pressure changes and flow surges within confined systems of incompressible fluids, practitioners in the art have provided a variety of devices known generically as pulsation dampers or accumulators. While the individual structures of such accumulators vary substantially, they typically provide among their other components a closed vessel coupled to the fluid system and containing a quantity of the system fluid as well as a confined volume of a compressible fluid or gas under pressure arranged such that the volume of incompressible fluid within the accumulator may rapidly change relying upon the compressible fluid to absorb or discharge the incompressible fluid as pressure surges and pressure changes within the system occur.
U.S. Pat. No. 4,186,776 issued to Burton sets forth a PULSATION DAMPENER OR SURGE ABSORBER which includes a pressure vessel having a diaphragm or bladder disposed therein for forming two noncommunicating zones within the vessel. The first zone is coupled to the incompressible fluid while the second zone is precharged with a compressible fluid. The bladder is of the reverse folding type and is provided with shock absorber means and an inlet bridging disk to protect the diaphragm when the pulsating fluid pressure is reduced.
U.S. Pat. No. 3,483,893 issued to Morley sets forth a HYDROPNEUMATIC ACCUMULATOR having a pressure vessel which supports a flexible bladder arranged to receive a relatively incompressible hydraulic fluid on one side of the bladder and a precharge of compressible fluid on the other side. The pressure vessel and the bladder are elongated; and support means within the pressure vessel provide positioning support for the bladder.
U.S. Pat. No. 3,115,162 issued to Posh sets forth an ACCUMULATOR in which an elongated generally cylindrical cylinder forms a pressure vessel having a central passageway enclosed by a rubber sleeve and having a chamber thereabout containing a compressible gas under pressure. The incompressible fluid is coupled to the interior of the rubber sleeve such that the compressible gas confined between the outer chamber and the rubber sleeve impart a pressure against the incompressible fluid. The configuration of the rubber sleeve changes to accommodate pressure changes and surges within the incompressible fluid.
U.S. Pat. No. 3,893,485 issued to Loukonen set forth a PULSATION DAMPENER which includes an elongated pressure chamber having therein a bladder assembly having a bladder which retains its surface area during pulsation dampener. The bladder is axially and longitudinally symmetrical. The bladder assembly comprises a bladder double-sealed at both longitudinal ends by a metal plate to prevent leakage. Pulsation changes cause the bladder to assume a clover leaf cross-sectional configuration.
U.S. Pat. No. 4,084,621 issued to Sugtmura sets forth an ACCUMULATOR CONSISTING OF WELDED VESSEL AND LID in which the pressure vessel of the hydraulic accumulator comprises a bowl-shaped body and lid member welded together edge to edge. A bowl-shaped diaphragm is supported by a rigid ring within the interior of the pressure vessel.
U.S. Pat. No. 273,379 issued to Miller sets forth a DEVICE FOR PREVENTING HAMMER IN WATER PIPES comprising an elongated flexible tube predisposed to curl into a helix and which is in communication with a pressurized water system. The helical tube uncoils in response to increased water pressure.
U.S. Pat. No. 2,721,580 issued to Greer sets forth a BLADDER TYPE PRESSURE ACCUMULATOR having an elongated pressure vessel supporting an elongated flexible bladder therein. One end of the pressure vessel is sealingly connected to the bladder and supports a valve for precharging the bladder with a quantity of compressible fluid. The other end of the bladder supports a valve arrangement for communicating the remaining portion of the accumulator to the incompressible fluid system.
U.S. Pat. No. 4,166,478 issued to Sugimura, et al. sets forth an ACCUMULATOR having a bladder to be filled with liquid in which an elongated pressure vessel supports a valve at one end which permits the vessel to be precharged with a quantity of compressible fluid and a coupling at the other end which is sealingly coupled to an elongated bladder within the vessel interior and to the system utilizing the incompressible fluid. The bladder extends upwardly within the vessel interior and divides the vessel interior into inner and outer compartments to separate the compressible fluid from the incompressible fluid. An inverted cone-shaped member is supported within the bladder and cooperates with a perforated rigid shell at the inlet to the interior of the bladder to prevent damage to the bladder during rapid discharge of the incompressible fluid.
U.S. Pat. No. 3,277,925 issued to Suglmura sets forth an ACCUMULATOR in which an elongated pressure vessel supports an elongated flexible bladder and is sealingly coupled to a charging port at the top of the vessel which permits the precharging of the bladder with a quantity of compressible fluid. A valve at the lower end of the pressure vessel is communicated to the system utilizing the incompressible fluid whereby the precharged compressible fluid within the bladder exerts a pressure against the incompressible fluid.
U.S. Pat. No. 3,091,258 issued to Marette sets forth a HOSE ACCUMULATOR in the form of an elongated hydraulic hose having an axially extending internal diaphragm which separates the hose interior into a hydraulic chamber and a compressible gas chamber extending lengthwise along the full length of the hose. The gas chamber is coupled to a inlet permitting the precharge of the gas chamber with a compressible gas while the hydraulic chamber is coupled to the hydraulic system. The chambers are separated by the internal diaphragm which flexes and changes shape without stretching to accommodate the proportional change in volume of the two chambers.
U.S. Pat. No. 4,174,741 Issued to Parsons, et al. sets forth METHODS FOR LOADING AND UNLOADING LIQUIDS FROM A RAILROAD TANK CAR in which an elongated closed tank car is provided with a pair of inlet ports and a pair of outlet ports and a flexible member sealingly dividing the tank car interior such that one set of inlet ports are disposed on one side of the sealing divider while the remaining set of inlet and outlet ports are positioned on the remaining side. The sealing divider is moved to one side of the tank car interior by filling the tank car through one of the inlet ports and is movable to the opposite side of the tank car interior when the tank car is filled through the other inlet port. Thus, the tank car is capable of carrying two different fluids at different times without the need of expensive cleaning of the tank car interior as each different fluid is used due to the division provided by the sealing member.
While the foregoing described hydraulic accumulators provide various levels of performance in accommodating and absorbing pressure changes within hydraulic systems, they are often subject to one or more problems associated with the use of the flexible bladder. For example, the flexing and movement Of the bladder within the pressure vessel frequently causes substantial wear of the bladder and ultimately results in fracture thereof which of course renders the accumulator unusable. By way of further example, a problem arises in the prior art accumulators when the incompressible fluid is completely exhausted from the accumulator. Under such conditions, the pressure of the compressible gas precharge often forces the bladder against the inlet with sufficient force to damage it and render the accumulator inoperative. While the foregoing systems which are representative of the prior art have attempted through various means to meet this problem, it is believed that a need continues in the art for an improved hydraulic accumulator which better resists the abrasion of the bladder and the damage thereto resulting when the accumulator is exhausted of hydraulic fluid.
While bladder type accumulators have provided considerable benefit in accommodating pressure changes and pressure surges within hydraulic systems, the use of the flexible bladder within the pressure vessel has been subject to a number of problems. One of the more common problems associated with bladder type hydraulic accumulators arises from the general wear and abrading which occurs as the bladder is subjected to being wrinkled, folded and often crushed within the pressure vessel during periods of operation in which a substantial amount of the hydraulic fluid is discharged or drawn from the pressure vessel. The wrinkling, twisting and abrading reduces the bladder life by causing it to rupture and requires that the hydraulic accumulator be discarded or repaired.
Other problems arise during system operations in which a high flow rate during discharge of hydraulic fluid from the accumulator takes place. With little or no hydraulic fluid left in the accumulator, the precharged compressible gas exerts an expanding force upon the bladder driving it against the fluid outlet of the accumulator. In the event the discharge rate of hydraulic fluid is high enough, the force imparted to the bladder by the compressed charge of gas can drive a portion of the bladder against the hydraulic fluid outlet and in some cases expel part of the bladder material out through the hydraulic fluid inlet port. This phenomenon known as extrusion of the bladder can destroy the bladder and contaminate the hydraulic system.
To meet this problem of bladder extrusion, practitioners in the art have provided various mechanisms which are intended to plug or close the hydraulic fluid port under conditions which would otherwise produce bladder extrusion. One of the most common systems provides a button or plug secured to the end of the bladder so that the plug is driven into the hydraulic fluid inlet port during operations in which substantially all of the hydraulic fluid is discharged from the accumulator. The problem with such button or plug systems is alignment. The folding or wrinkling of the bladder during hydraulic fluid discharge is generally imprecise and misalignment between the plug and the hydraulic fluid inlet port often causes the plug to fall to seal the inlet port. Another attempted solution to extrusion uses a popper valve device positioned within the hydraulic fluid inlet port which senses high flow discharging and closes to isolate the accumulator from the hydraulic system. While this popper valve system protects the accumulator, it functions to isolate the hydraulic accumulator from the hydraulic system at precisely the time it is most needed and therefore is generally unsatisfactory.
Still other problems result in the use of such hydraulic accumulators in their preference for functioning best with a vertical axis. Because the hydraulic fluid within the accumulator is a liquid subject to being repositioned due to gravity forces and because the flexible bladder charged with a compressible gas tends to float within the hydraulic fluid, the operation of hydraulic accumulators generally requires that the accumulator be maintained in a substantially vertical orientation.
The various problems associated with bladder malfunction when the accumulator is operated with most of the hydraulic fluid discharged from the accumulator have prompted hydraulic system designers to substantially oversize the hydraulic accumulators within a system to provide a safety factor or margin for reliable system operation. This oversizing of hydraulic accumulators substantially increases the cost of the hydraulic system equipment. In addition, it is often inconvenient to utilize an oversized accumulator due to space restrictions.